Certain retroviruses and herpesvirus naturally and commonly infect and cause cancer in chickens and turkeys. These viruses include some of the most potent cancer-causing agents known in animals. Human exposure to these agents is virtually universal, and occurs through: 1) contact with live poultry;2) contact with their blood and raw meat and egg products;3) through ingestion of raw or inadequately cooked poultry meat and eggs;4) occupationally in jobs such as raising, slaughtering, processing, and sale of raw poultry products, veterinarians, poultry inspectors, cooks, laboratory scientists, etc.;5) inoculation with vaccines manufactured by growing the vaccine virus in chicken embryos such as measles, mumps, influenza, and yellow-fever vaccines, that may contain exogenous and endogenous forms of these oncogenic viruses. It is known that the viruses can infect human cells in vitro and transform them into cancerous cells, and experimentally the viruses can infect and cause tumors in primates. Furthermore, serological tests in humans clearly indicate widespread infection of the general population with these viruses. However, definitive proof that the viruses cause cancer in humans is currently lacking partly because of the absence of analytic epidemiologic studies of cancer risk in exposed individuals. We hypothesize that if these viruses cause cancer in humans, it will be most readily evident in workers in poultry slaughtering &processing plants who have the highest human exposure to these agents. Accordingly, we conducted cancer mortality studies in three separate cohorts of these workers. The results indicate excess occurrence of 16 cancer sites. The proposed investigation is a case-cohort study of 13 of these sites to investigate the role of these viruses in their etiology, while controlling for and concurrently investigating the roles of other potential occupational and non-occupational carcinogenic exposures. Infectious diseases, is one of the priority areas identified by NIOSH in its Occupational Safety and Health Research program. Public Health Relevance: Certain viruses naturally infect and cause cancer in chickens and turkeys. Humans are commonly exposed to these viruses from contact with live chickens and turkeys and their blood and secretions, or from eating raw or inadequately cooked poultry products, including eggs. Also, humans are exposed to these viruses when they are vaccinated with vaccines manufactured using chicken eggs, such as measles and mumps vaccines. However, it is not known if these viruses cause cancer in humans. To find out, we are conducting a study of persons who work in places where chickens and turkeys are killed and processed, who have the highest human exposure to these viruses. Thus if these viruses cause cancer in humans this should be easily seen in this group. The study will also determine if other agents which these workers are exposed to at work such as smoke during the smoking of meat or fumes during wrapping of meat that contain chemicals which are known to cause cancer in humans, are also causing cancer in these workers.